The present invention relates to devices for cleaning the inner walls of tubes and, in particular, to fluid driven projectiles used for cleaning condenser tubing and the like.
It is known that the cleaning of the inner walls of condensers and similar tubes can often be facilitated by driving a projectile having an attached scraper element through a tube with sufficient force so that the scraper element removes mud, slime, scale or other accumulated material from the tube wall. These scraper elements usually consist of one or more blades, bristles, or pieces of wire which extend perpendicularly from a forward elongated body section of the projectile so that, when the body section is disposed longitudinally in the tube, the scraper element is in contact with the tube wall. The body section, itself, is connected to a rearward head or terminal section which is usually cylindrical in shape and of a diameter that is somewhat less than the inner diameter of the tube. Thus, when the projectile is inserted, body first, into the tube opening and when sufficient fluid pressure is exerted on the rearward surface of the terminal section, the projectile will be driven before this fluid pressure through the length of the tube. In this way, the interior of the tube is cleaned by the projectile without need of any attached and externally manipulated lines or handles. Tube cleaning projectiles of this nature are described, for example, in U.S. Pat. Nos. 1,598,771, 2,170,997, and 2,734,208.
It is desirable that the diameter of the terminal section should approach the inner diameter of the tube, since where the gap between the terminal section and the inner wall of the tube is excessive, a large part of the propelling fluid may leak past the terminal section so that the fluid is lost for the purpose of driving the projectile. Notwithstanding the importance of minimizing the amount of fluid pressure which is lost in this manner, it is found that the maintenance of relatively tight seal between the projectile and the inner wall of the tube may not be feasible with many of the tube cleaning projectiles currently in use. That is, where the edge of the terminal sections of these projectiles is in close proximity to the tube wall there may be a danger that the forward motion of the projectile will be obstructed by irregularities in the tube wall. These irregularities may consist of dents in the tube wall or, as is more commonly the case, of insert obstructions, which are plastic tubular inserts placed in the tube at its opening for tube protection purposes. These insert obstructions abut the inner wall of the tube over a portion of its length and thereby effectively reduce the inner diameter of a tube over that length so as to make certain types of projectiles inefficient.
For example, the rigid, substantially flat terminal section shown in the projectile disclosed in U.S. Pat. No. 2,170,997 would not bend so as to pass an obstruction. When such a projectile is used to clean a tube in which an insert obstruction has been emplaced, the diameter of its terminal section must be less than that of the inner diameter of the insert obstruction. Thus, after the projectile passes the insert obstruction, the gap between the edge of the terminal section and the tube wall would increase so as to result in a loss of fluid pressure on the terminal section.
The projectile disclosed in U.S. Pat. No. 1,587,771, on the other hand, has a terminal section which is flared back so that, if sufficient fluid pressure were applied to the terminal section, it might be possible to axially compress or crush the terminal section so as to allow it to pass over an obstruction. There is, however, no indication that the terminal section disclosed in this patent has any feature which would enable it to recover its original form after it had been compressed in this manner so that fluid pressure might thereafter be lost by reason of the resulting deformation in the terminal section.
U.S. Pat. No. 2,734,208 discloses a projectile in which a rubber ring extends perpendicularly outward from the peripheral edge of the terminal section. While this ring may flex and then recover its original shape, certain disadvantages may also be associated with this design. That is, because it extends perpendicularly outward from the terminal section, the rubber ring may be pressed by the fluid on its rear side against an obstruction so that the flexing of the ring to the extent which would be necessary to bypass that obstruction might be impeded or prevented.
It is therefore an object of the present invention to provide a tube cleaning projectile which has a terminal section that has a sufficiently tight seal with the inner wall of the tube so as to allow for efficient use of its propelling fluid but which also easily flexes so as to allow it to pass obstructions in the tube.